The die-cast product of a light alloy is manufactured by forcing the melt of the light alloy into a cavity in a pair of dies consisting of a die segment and a stationary die. A sleeve is connected through the medium of a bush to the cavity and an injection mouth formed in the sleeve is used for admitting the molten alloy. The incoming molten alloy is forced into the cavity with a plunger. In the die casting machine to be used for manufacturing die-cast products as described above, generally tool steel, SKD61, is used as the material for forming the sleeve.
In the die casting of such light alloys as mentioned above, it has been recently brought to light that particularly when the die casting machine adopted happens to be of the cold chamber type, the fall of the temperature of the molten alloy introduced into the cavity greatly affects the quality of the die-cast product. Specifically, it has been heretofore customary to cool the periphery of the sleeve for the purpose of protecting the sleeve against the heat of the molten alloy. The temperature of the molten alloy, therefore, is lowered and part of the molten alloy forms a solidification phase and the solidification phase directly leaks into the die-cast product, degrades the mechanical property and the air-tightness of the machine, or induces the occurrence of furrows on the product surface. It has been also found that when the sleeve is not subjected to forced cooling, insufficiency of the amount of the molten alloy to be injected into the sleeve enlarges the fall of the temperature and impairs the quality of the die-cast product.
For the solution of the problems mentioned above, the wisdom of heating the periphery of the sleeve to preclude the advance of solidification within the sleeve is being studied. By heating the periphery of the sleeve, the solidification phase can be prevented from entering the die-cast product. Since the heating tends to induce deformation of the sleeve, it ultimately degrades the durability of the die casting machine. The measure resorting to the heating still has the problem of impracticability because the material for the sleeve which is capable of overcoming such drawbacks as mentioned above has not yet been found.
The feasibility of using a ceramic material of excellent insulation and low thermal expansivity in part of the sleeve is also being studied. The ceramic material, however, has poor reliability of performance because it is deficient in shock resistance and rigidity. This measure has such problems as inflicting a crack on the interface because of a large difference in thermal expansion coefficient between the ceramic material and the material of the peripheral part. It further has a serious practical problem that the ceramic material is not easily molded in a complicated shape.
It has now become necessary that the material for the sleeve to be used in the die casting machine should acquire further improved thermal insulation and exhibit a small difference in thermal expansion coefficient from the plunger and the peripheral retaining parts thereof. The methods and the materials which have been heretofore used for the sleeve, therefore, are no longer capable of fulfilling the necessity mentioned above.
An object of this invention is to provide a sleeve for a die casting machine which offers high thermal insulation, possesses the ability to preclude entry of a solidification phase, and excels in reliability of performance, namely a sleeve for a die-casting machine which acquires enhanced durability. Another object of this invention is to provide a sleeve for a die casting machine which allays the difference in thermal expansivity from the peripheral parts and exalts the reliability and durability besides fulfilling the aforementioned conditions, namely a sleeve for a die casting machine which enjoys perfect castability and machinability. Still another object of this invention is to provide a die casting machine which, owing to the use of the sleeve of the quality mentioned above, enjoys improved yield and, at the same time, excels in durability and reliability.